1. Field of the Invention
The present invention relates to retainers for electronic modules, in particular, to retainers which allow rapid, easy, and tool-free installation and removal of electronic modules.
2. Description of Related Art
Electronic modules, such as printed circuit boards, are frequently mounted in casings having two opposing parallel walls. The walls are provided with corresponding slots which receive opposite edges of the electronic module so that the module is supported, like a tray, between the opposing walls. Typically in such a configuration, the width of the slots is greater than the thickness of the electronic module. This size disparity allows for easy insertion of the modules and allows the slot to accommodate modules of varying thicknesses.
However, as a result of the loose fit of the module within the slot, if the module is not held firmly within the slot, the module is more susceptible to damage resulting from vibration or shock. Further, such casings are frequently designed as heat exchangers, commonly called cold plates, to dissipate heat generated by the electronic module. For the casing to work efficiently as a heat exchanger, it is desirable to maintain the electronic module in firm contact with the casing to provide a reliable thermal path and improve the heat transfer between the electronic module and the casing.
To reduce damage to the electronic module resulting from shock, vibration, and poor heat transfer, retainers have been developed to clamp electronic modules firmly against an edge of the casing slots. U.S. Pat. Nos. 3,767,058 to Barlow et al. and 4,298,904 to Koenig each describe retainers having wedge-shaped elements received on a threaded rod. These retainers can be inserted into the slot with the electronic module. The threaded rod is then turned to bias the wedge-shaped elements which slide along the faces of the wedges-shaped elements to exert a clamping force lateral to the axis of the rod to maintain the electronic module firmly within the slot.
However, with this type of retainer, it is necessary to turn the threaded rod to tighten or loosen the electronic module each time it is desired to insert or remove the module. This is tedious and time consuming, and typically requires a separate tool. As a result, installation or removal of the module is inconvenient and may be thwarted if the appropriate tool is not readily available.
One type of available retainer uses wedge-shaped elements and allows for tool-free insertion and removal by providing a lever operated cam surface for biasing the wedge-shaped elements. However, with this device, as well as the other devices described above, it is possible for the wedge-shaped elements to rotate about the rod and become misaligned. Should this occur the retainer will be inoperable unless the elements can be properly oriented, a task which is not always simple given the limited access frequently imposed by the environment in which the retainers are used.
A retainer having wedge-shaped elements in which the elements are prevented from rotating is described in U.S. Pat. No. 4,480,287 to Jensen. However, this retainer requires the rotation of a threaded element to bias the wedge-shaped elements. As a consequence, this retainer, and other similar retainers, suffer from the previously described drawbacks associated with such a system.
U.S. Pat. No. 4,414,605 to Chino et al. describes a retainer having a wedge-shaped element received on a threaded rod. A pivotal driver blade is provided for turning the rod which is received by a threaded aperture in the case. The pivotal driver blade has a cam surface which, when the driver blade is pivoted, biases the wedge-shaped element. However, this device requires a special casing having a threaded aperture for receiving the threaded rod. In addition, this device still includes the tedious and time consuming step of rotating the rod every time the electronic module is installed or removed.
None of the devices described above provides positive extraction force to facilitate removal of an electronic module. Such a positive extraction force is desirable because typically one end of the electronic module is plugged into a connector which often has a high retention force. In addition, it is possible for the electronic module to adhere or stick to the slot, particularly when the module has been tightly clamped against the slot for an extended period of time. Alternatively, the electronic module may become wedged or jammed in the slot. As a result, merely loosening the retainer may not be enough to facilitate easy removal of the electronic module.
The clamp arrangement described in GB 2,101,812A shows a system of levers attached directly to a printed circuit board. A first lever includes a projection which contacts the casing to extract the printed circuit board when the first lever is rotated. Rotation of the first lever also controls a second lever, also mounted directly to the printed circuit board, which actuates a clamp mechanism made of alternating large and small cylinders in a staggered arrangement. This clamp arrangement includes a large number of intricate parts which make the clamp expensive, difficult to manufacture and assemble, and more prone to failure.